This invention relates to the provision in a metallurgical vessel, e.g. a tundish, of refractory linings and flow control devices.
It is well known to line tundishes and the like with a permanent lining of refractory material, e.g. refractory brick, adjacent the metal casing of the tundish and an expendable inner lining of refractory, heat-insulation material. This expendable lining is normally applied in slab or sheet form, the slabs being introduced to form to the floor and walls of the tundish. [See, for example, U.S. Pat. Nos. 4,012,029; 4,022,358; 4,042,229; 4,043,543; 4,048,134; 4,245,761; 4,330,107; 4,055,336; 4,076,224; 4,126,301; 4,158,939; 4,165,026; and 4,194,730.] Such a lining for a typical tundish, which may have a capacity of from 2 to 80 tons of molten metal, is usually applied in a number of separate, preformed pieces that have been designed to fit the specific tundish being lined. Twenty or thirty or more separate pieces of lining may have to be fitted and their joints carefully sealed to prevent penetration of the molten metal between the lining and the metal casing of the tundish.
In addition to the large number of expendable lining pieces requiring to be assembled in the tundish, it is frequently necessary to incorporate various flow control devices, including dams, weirs and baffles to direct the flow of molten metal and to create whatever conditions of change of direction and turbulence that may be deemed desirable in a particular tundish.
It has also been proposed to apply the expendable lining as a one-piece integral unit by spraying a suitable composition onto the tundish floor and walls and allowing it to dry. Although this eliminates a lot of the labor-intensive assembly of the preformed shapes, such integrally-formed linings still cannot eliminate the need for separate assembly of the various flow control devices and erosion resistant slabs.
The present invention aims to provide advantages of both of the aforementioned types of linings and to reduce or eliminate the need for separate assembly of the flow control devices and erosion resistant slabs.
In one aspect, therefore, the invention provides a preformed expendable lining for at least a portion of a metallurgical vessel, the lining being integrally formed in one-piece and having a floor portion, wall portions and at least one integrally-formed flow control device.
The lining of the invention may be formed to line a part only of the vessel, hereafter referred to for convenience as the tundish. It is of particular value for so-called T-shaped tundishes (in which when viewed in plan, the cross-bar or top of the "T" corresponds to the main body of the tundish and so is of greater length than the tail or vertical of the "T"). The area inside the tundish in the region of the junction of the cross-bar and tail of the "T" is usually the pour area where molten steel is introduced into the tundish. This region, therefore, normally has a special erosion-resistant impact pad on the floor, and the side walls have erosion resistance and it is often desirable for some of the required flow control devices to be positioned as closely adjacent to this region as possible (e.g. the erosion resistant side walls).
In transverse cross-section both the "crossbar" and the "tail" sections or body of the tundish normally are of frusto-conical shape with the walls sloping outwardly as they rise from the floor. It is frequently desired to position upright, i.e. substantially vertically-extending transverse baffles of sufficient height to extend a considerable way up the walls of the tundish. Such baffles take the form of substantially planar slabs of similar or the same erosion-resistant material as the expandable linings and are provided with a series of through apertures or holes to allow molten metal to pass down the tundish. The positioning of such baffles and the size and spacing of their apertures are carefully arranged to control the metal flow, as is well known in the art.
Thus, it is frequently desirable to position a pair of such transverse baffles across the main body of the tundish, one on each side of the T-junction region but as close as possible to (and, of course, substantially parallel to) each of the walls defining the "tail" of the T-piece. Because of the angled nature of the walls of the tundish, it has conventionally been necessary to fix these vertical baffles at some distance from the T-junction. This results in the formation of a corner around which metal must flow to pass along the main body of the tundish. The expendable linings at such corners are necessarily subject to very severe erosion. The present invention enables such corners to be eliminated.
Accordingly, in another aspect, therefore, the invention provides a preformed lining for the pour region of a tundish, the lining being integrally-formed in one piece to include a floor corresponding to the pour region, walls corresponding to two opposed walls of the tundish in the pour region and at least one flow control device extending substantially at right angles to the said opposed walls.
In a specific preferred embodiment, the integral lining defines the pour region at the T-junction and comprises a floor portion and four walls, a first wall corresponding to the base of the tail of the "T", a second wall correspond to the portion of tundish wall directly opposed to the first wall, and third and fourth walls facing each other and extending between the first and second walls, the third and fourth walls having baffle portions which are provided with an arrangement of holes, the baffle portions extending across the transverse width of the main length of the tundish.
The invention, therefore, has considerable advantages over known linings and, moreover, offers unexpected advantages to outweigh what might be perceived as series disadvantages in such a one piece preform. Clearly, there are advantages in the reduction of the number of shapes that have to be positioned and sealed. For example, in the pour area of a typical tundish, a single preformed piece of the present invention can replace, say, eight or ten conventional wall and floor shapes plus two or more flow control devices. Human error can, thereby, be reduced and the risk of a faulty fitting or sealing greatly reduced. The likelihood of molten metal penetrating a joint and leaking and of a shape being "floated away" by the molten metal is, thereby, eliminated or great reduced.
Nevertheless, the proposed use of an integrally-formed unit might well be thought disadvantageous. Such a product is a large, three-dimensional, relatively fragile object whose storage, transportation and fitment would, apparently, be more difficult and troublesome than for a number of individual relatively planar pieces.
However, the further advantages particularly to be obtained from the integral-forming of the lining with the flow control devices for the pour area of a T-shaped tundish, as indicated above, will be further described below with reference to the drawings.
The material from which the one-piece lining with flow control device(s) of the invention may be formed are any suitable materials such as those conventionally used to line a tundish, i.e. based on mixtures of refractory fibers, alumina silica aggregates and calcium aluminate cement or other fillers and binders.
For example, calcium silicate or aluminum silicate fibers; silica, alumina, magnesia and refractory silicate fillers; and colloidal silica sol, starch, phenol-formaldehyde resin and urea-formaldehyde resin binders, mulcoa grains, bauxite or alumina aggregates may be used in combination with fines of fumed silicia and alumina with a calcium aluminate cement or other compatible binder systems. Mixtures of magnesia and particulate olivine are particularly useful refractory fillers. In a preferred embodiment, the one-piece lining is formed of 60-70% alumina, low moisture, low cement, high density, castable refractory material.
The devices can conveniently be cast into one-piece form from a slurry or a vibratable castable of the desired materials. Where the flow control devices are baffles with holes through which the molten metal in the tundish is intended to flow, the holes may be integrally-formed during the casting process by the incorporation of suitable pins or blanks in the positions corresponding to the holes. Alternatively, they may be cut or punched in the formed baffle.
According to another aspect of the present invention, there is provided a combination of a trough shaped tundish having a pour area and a lining. The lining is integrally formed of refractory material and comprises a floor portion and walls, and at least one flow control device (e.g. baffle, dam, or weir) built integrally therein, the lining being dimensioned to fit within the trough shaped tundish covering the pour area with the flow control devices controlling flow from the preformed lining to other areas of the tundish not lined by the preformed lining.
It is the primary object of the present invention to provide for the simple and effective lining of a metallurgical vessel with expendable material, particularly the pour area of a tundish. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.